The present invention relates generally to a method and apparatus for perforating a web in the cross machine direction. Additionally, the present invention relates generally to a method and apparatus for perforating a web in the cross-machine direction wherein the web includes elastic members extending in a machine direction.
In conventional perforating methods, a line of perforations is formed by cutting or punching through a web at spaced intervals to form a line of discontinuous cuts defined by cut segments separated by uncut regions. Conventional perforating is frequently undertaken with a standard knife and anvil system wherein the knife includes a plurality of notches in the cutting edge that corresponded to the uncut regions in the line of discontinuous cuts. In conventional perforating methods, changing the relative density and/or size of the cut segments and/or the uncut regions requires obtaining new knives having notches of the appropriate size and spacing to create the desired new pattern. Additionally, in conventional systems, as old knives become dull, new knives must be modified with the appropriate notch sizes and spacing to create the desired pattern.
Furthermore, conventional perforating methods are not optimal for perforating webs with elastic members or other reinforcing members extending in the machine direction because the elastics disposed in the cut segments are cut and the elastics disposed in the uncut regions remain whole and thus retain their strength. This provides an impediment to separation of the web along the line of perforation.
Furthermore, inherent variability in the cross-directional tracking of the web and cross-directional placement of the elastics results in a varying number of elastics being cut at various times. As such, the force required to break the web at the line of perforation also varies over time and causes difficulties in processing.
Therefore, there exists a need for a method and apparatus for perforating a web wherein the perforation pattern can be changed without changing the knife. There also exists a need for a method and apparatus for perforating a web wherein the knives do not need to be altered to achieve the desired perforation pattern. Finally, there exists a need for a method and apparatus for perforating a web having elastic members extending in the machine direction wherein each of the elastic members are consistently cut or damaged.